Real world trajectory data

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fishinwrench

fishinwrench

Member
Nov 25, 2017
589
16
mo
After a lengthy chronograph session, or more like 5 of them, the trajectory data on chairgun and strelock wasn't accurate, so here's what I did...... 
I carefully shot a 5 shot group at 30yds and another at 40yds, then accurately measured the drop. I then pulled up Chairgun, entered my projectile and scope height data and then altered the FPS until the drop between 30 and 40 yds. matched the ACTUAL drop measurement.
Ureaka! My trajectory chart is now spot on at all ranges, and I mean DEAD ON from 15 to 75 yards (and probably beyond, but 75 is as far as I will ever shoot).

Now, whether chronographs (even the very good ones) are bullpoop, or the B.C. is the reason......it doesn't matter. Who needs a damn chronograph if the numbers are unreliable ? The real world FPS of my set-up is 86 FPS different than what the best chronograph on the market says it is.
 
"fishinwrench"Now, whether chronographs (even the very good ones) are bullpoop, or the B.C. is the reason......it doesn't matter. Who needs a damn chronograph if the numbers are unreliable ? The real world FPS of my set-up is 86 FPS different than what the best chronograph on the market says it is.
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This happens because the BC of the pellet changes with a whole host of factors. BC is velocity dependent, meaning that it changes as the pellet looses velocity. BC is changed by anything which changes the shape of the pellet, so number of lands and grooves, actual bore diameter, for example. BC changes when air density changes, thinner air (higher altitude) better BC, thicker air (lower altitude) worse BC. Humidity is a factor... etc.. yada yada. You can't get exact results by using the BC numbers that Chairgun provides. They are there to give you a starting point. The method you have just used is quite valid and you could compute your true "average" BC from the information you have now collected, or let Chairgun do it for you. ;) Good thinking.
 
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"Oregun"Very interesting!
Was the 86fps high or low? What are you shooting (gun & cal)?
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My real world velocity is lower than the high dollar chrony showed. Of all the chrony testing I have done, believe it or not, that stupid Chrono--connect app on my phone is the closest to my real world calculations (which according to chairgun and my POI at different ranges, is 100% balls-on accurate).

I've been at this since 10:am this morning. Three different guns /w 4 different pellets. Results are the same on all. I'm happy as can be. I don't give 2 poops what the true BC is, nor do I care what my TRUE velocity is , as long as I can hit dead on at all known ranges consistently. To me that's all that matters. And this backwards method flat works.
 
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86b3e811931176b4e0f7b4970a9c2be5.jpg
This is my drop chart. I manipulate Chairgun untill it matches. I change the scope power instead of velocity or bc. It's a long complicated story how it works for me but it works. Have fun, Scott
 
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I had a similar experience this past weekend. I haven't shot in about 2 months and was sighted in for my backyard at 17ds. It was dead nuts on at various ranges using chairgun the last time I shot at 50, 70, 90. 

Last Saturday, my buddy, Dave and I headed out to the coast range for a day of shooting. We set targets at 50, 62 & 85 yrds. I shot a few strings at 50 without making any adjustments. I was hitting high with nice groups, I then made my adjustment according to the App. very slight shift, not what I was expecting as it was still high and tight. After 30 or 40 minutes of hair pulling, I shot at the 62 yrd target. It was close to target. Just a couple clicks, I was spot on.

Long story short, I used holdover at 85 and 50 the rest of the day. The variables or differences from that day include, elevation (2000ft), crystal clear, no humidity, temps in the 50's. (perfect conditions!). My theory was my gun was shooting hot 
9e7523a05204db511e37d8c76638df60.jpg
f1f74fb9fb76ec21078d95a172950116.jpg
5f7f8c1cc4ee194edc857e765ed675b0.jpg

I’m mystified...
 
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"fishinwrench"
"Oregun"Very interesting!
Was the 86fps high or low? What are you shooting (gun & cal)?
Click to expand...

My real world velocity is lower than the high dollar chrony showed. Of all the chrony testing I have done, believe it or not, that stupid Chrono--connect app on my phone is the closest to my real world calculations (which according to chairgun and my POI at different ranges, is 100% balls-on accurate).
I've been at this since 10:am this morning. Three different guns /w 4 different pellets. Results are the same on all. I'm happy as can be. I don't give 2 poops what the true BC is, nor do I care what my TRUE velocity is , as long as I can hit dead on at all known ranges consistently. To me that's all that matters. And this backwards method flat works.
Click to expand...
Have you tried with Strelok Pro doing the same thing that with Chairgun but after firing an making test for drop at longer ranges you go to the "truing" option inside the app and with all that the app makes somekind of cross-reference between your theoretical chart values (given by the app at the beginning) and the real world results to give you the best possible outcome.
I remember that Matt Dubber has a youtube video on the process in his channel, in that episode his shooting a .260 REM to about 700 meters, check it out it might help or not......at least you can compare it with your method and let us all know, thanks!

Alejandro
 
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"Oregun"I had a similar experience this past weekend. I haven't shot in about 2 months and was sighted in for my backyard at 17ds. It was dead nuts on at various ranges using chairgun the last time I shot at 50, 70, 90. 
Last Saturday, my buddy, Dave and I headed out to the coast range for a day of shooting. We set targets at 50, 62 & 85 yrds. I shot a few strings at 50 without making any adjustments. I was hitting high with nice groups, I then made my adjustment according to the App. very slight shift, not what I was expecting as it was still high and tight. After 30 or 40 minutes of hair pulling, I shot at the 62 yrd target. It was close to target. Just a couple clicks, I was spot on.
Long story short, I used holdover at 85 and 50 the rest of the day. The variables or differences from that day include, elevation (2000ft), crystal clear, no humidity, temps in the 50's. (perfect conditions!). My theory was my gun was shooting hot 
9e7523a05204db511e37d8c76638df60.jpg
f1f74fb9fb76ec21078d95a172950116.jpg
5f7f8c1cc4ee194edc857e765ed675b0.jpg

I’m mystified...
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I feel you aren't giving mother nature her due in it's interaction with your ballistics. You say it was in the 50's. Shooting from shade into sunlight over melting snow means there is some humidity in the air as the snow is evaporating from the temperature, and even more so from the sun. This will create differentiating thermals affecting your projectiles flight path. I'm honestly surprised you didn't catch a mirage in your scope at the point where the shade and sun meet. That can also cause what appears to be a shift in the optics. Of course your gun could have been shooting hot, or gotten knocked or bumped to cause a shift but I think given your location and the weather/range conditions there's enough mother nature there to mess with ya.
 
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Based on this thread, I can see now why Ted Bier likes his MTC scopes so much. Just 
make a range tape for the top turret and your done. I pest mostly at home, and have all the ranges mapped out in my head. I think I will try a Viper pro since I am in the market for a new scope, and I don’t want or have time to screw around with calculations when I need to take shots quickly. 👍🏿
 
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